Modern materials present a number of formidable challenges to the fabricators of a wide range of optical, semiconductor, and electronic components, many of which require precision shaping, smoothing, and polishing. The use of plasmas to etch materials has become an important technique in the optical component and semiconductor industries. Recent advances have introduced sub-aperture plasma processes, such as reactive atom processing (RAP), which act more like traditional machining tools by etching only specific areas of a workpiece.
A plasma etching process differs from its mechanical counterpart by the mechanism in which material is removed. Traditional machine tools use mechanical parts to physically cut away material from a workpiece. Plasma etching processes, on the other hand, rely upon chemical reactions to transform the solid material of the workpiece into a volatile or otherwise labile byproduct. Plasmas offer advantages such as the contact-free removal of material, in which little to no force is extered on the workpiece. Reliance upon a chemical means of material removal introduces a whole new set of factors to consider when treating a material.
A RAP torch can be used to determinalistically shape and polish surfaces using a plasma or a flame. The discharge emitted from the RAP torch can remove material for the surface of a workpiece, somewhat analogous to the end mill used in traditional machining. The footprint of a typical RAP torch tool is roughly Gaussian in shape, and has a size that can be determined by the inside diameter of the outer tube that contains and directs the plasma host gas or non-reactive species.
In traditional machining, a variety of tool shapes and sizes are required. For maximum utility, machine tools have been designed to allow rapid interchange of bits and cutters. This approach is also possible with a RAP tool, but the presence of induction coils tends to complicate the changeover. Before any shift occurs, the unit must cool down and the enclosure must be purged of any dangerous fumes. The gas lines to the torch must be disconnected to remove the torch assemby and then purged before a new unit is installed. Depending on the size and type of the new torch, it may be necessary to replace coils used to generate the inductively coupled plasma (ICP). Once the torch assembly and coils have been swapped, the entire setup must be meticulously realigned and tested in order to assure proper function.